The concept of producing plied yarns using the false-twist, self-twist phenomenon are now rather well known in the art. Documents in which the general principles of false-twisting and self-twisting are described include the following:
"Self-Twist Yarn," D. E. Henshaw, Merrow Publishing Co., Ltd., Watford, Herts, England, 1971 PA1 U.S. Pat. No. RE 27,717--Breen et al. PA1 U.S. Pat. No. 3,225,533--Henshaw PA1 U.S. Pat. No. 3,306,023--Henshaw et al. PA1 U.S. Pat. No. 3,353,344--Clendening, Jr. PA1 U.S. Pat. No. 3,434,275--Backer et al. PA1 U.S. Pat. No. 3,507,108--Yoshimura et al. PA1 U.S. Pat. No. 3,717,988--Walls PA1 U.S. Pat. No. 3,775,955--Shah PA1 U.S. Pat. No. 3,940,917--Strachan
For purposes of convenience, some general comments concerning producing plied yarn by these techniques will be described. It is possible to form a plied yarn by false-twisting two or more singles yarn strands, attaching the strands to each other and then permitting the strands to wrap about each other using the release of forces stored by the false-twisting to accomplishing the plying, hence the term "self-twist". The false-twisting itself, in simplified form, involves holding spaced points of a yarn strand and twisting the strand in one direction at a point intermediate the held points, e.g., the center. This produces twists on one side of the center in one direction and on the other side of the center in the opposite direction. The center of the twisted strand constitutes a point of twist reversal and is called a "node". Clearly, forces are stored in the strand in the twisting step. When two strands similarly false-twisted are brought together in side-by-side juxtaposition and permitted to act against or with each other by releasing the nodes, the stored forces cause the strands to ply, i.e., to wrap around each other spontaneously. The process is enhanced and the product made more stable if the nodes of the two strands are aligned and are joined or locked together before release and plying.
As will be recognized, the torque or twist force exerted by each strand is roughly proportional to the amount of twist therein and that such force decreases as the strands ply. The plying step itself therefore continues until the stored twist forces in each strand decrease to a point at which the remaining twist forces are exactly counterbalanced by the resistance to further twisting in the plied yarn. Thus, if one begins with individual strands and then false twists the strands and plies them, each strand will end up, in the plied yarn, with some degree of false-twist which can be thought of as some remaining stored potential energy, the force exerted thereby being too small to cause further ply twisting against opposing frictional forces in the plied yarn. The resulting degree of ply twist is thus proportional to the amount of false twist imparted to the singles yarns.
An apparatus for false-twisting and node fastening and plying singles yarn strands is fully described in U.S. patent application Ser. No. 755,671, filed Dec. 30, 1976, now U.S. Pat. No. 4,074,511, wherein a rotatable guide member receives the false-twisted yarn and fastens the nodes thereof using a rotating contact device carried by the guide member.
As described in that application, and as partly shown in FIG. 1, the apparatus for forming and initially false-twisting the strands, the system commences with the yarn strands being withdrawn from sliver containers 10 and 11, the yarn strands 12 and 13 being subjected to a drafting or drawing process by pulling the yarns between drafting rolls, yarn 12 being drawn by drafting rolls 14 and 15 and yarn 13 being drawn by rolls 16 and 17. Roll 15 is typically driven at a surface velocity greater than that of roll 14 and roll 17 is driven at a surface velocity greater than roll 16. The yarns can then be passed through primary twist jets, yarn 12 being passed through jet 18 and yarn 13 being drawn through jet 19. The primary twist jets operate to impart and maintain twist at the critical point where the otherwise flat sliver ribbon leaves the draft delivery rolls. Yarn strand 12 is then passed through a singles-twist jet 20 and yarn 13 is then passed through a singles-twist jet 21 wherein the false-twist is inserted in the yarn strands. Air pressure under the control of apparatus not shown in FIG. 1 is supplied to false-twist jets 20 and 21 through conduits 22 and 23, respectively.
The control apparatus for the air supplied to jets 20 and 21 may be fluidic valves, electrical valves or mechanically operated valves which alternately supply fluid under pressure to the conduits of the false-twist jets so that the singles strands are sequentially twisted alternately in S and Z directions. It should be noted at this stage that jets 20 and 21 are paired to twist the yarn strands in the same direction as each other and are operated to periodically reverse the direction of twist to result in producing a yarn wherein there are opposite senses of twist separated by short nodes of zero twist, which nodes are in synchronization with the yarn wheel which bears a fixation device so that the nodes appear at the surface of the fixation disc at the appropriate time. Thus, yarn strands 12 and 13 emerge from jets 20 and 21 with alternating S and Z portions of twist therein.
The strands are then passed through a wire guide which can constitute a single elongated wire guide 24, or which can include separate wire guides associated with jets 20 and 21. The wire guide in either form assists in maintaining the singles twist in the yarn strands and serves the purpose of bringing the yarn into a relatively closely spaced relationship, preferably not in contact with each other. The yarns are guided onto a yarn wheel indicated generally at 24, the details of which will be described hereinafter. Yarn wheel 25 serves the function of guiding the yarns in parallel spaced relationship with each other, fixing the yarns at their nodes by means of a rotating fixation device, along with appropriate guides.
After the yarn has been twisted and the nodes locked on yarn wheel 25, the yarn 27 is passed around an idler roller 28, the singles yarns plying or self-twisting together at they leave the yarn wheel 25. If desired, the plied yarn can be passed through a heatset tube 29 and a further idler roller and then collected as indicated at 30.
The yarn wheel, which is also shown in application Ser. No. 755,671 and which is usable in the apparatus of FIG. 1, is illustrated in FIGS. 2 and 3 and includes a generally disc-shaped member having flanges 35 and 36 at the axial limits thereof and a central, separatory flange 37, the three flanges defining peripheral surface portions 38 and 39 along which yarn strands can be separately guided. Although wheel 25 is shown as having a single central, separatory flange 37, additional separatory flanges may be provided depending upon the number of singles yarns being plied. The number of separatory flanges will always be one less than the numbers of singles yarns being plied. Central flange 37 is interrupted at 40 to permit the strands to come into close proximity with each other and also to come in contact with the contacting surface of the fixation device which, in the illustrated embodiment, is an abrasion disc 41 which is rotated about an axis generally perpendicular to the axis of rotation of the yarn wheel and at a relatively high speed, on the order of 8,000 rpm. Typically, the disc can be driven by an electric motor which is mounted in the yarn wheel and to which DC voltage is supplied by means of a brush and slip ring combination, not shown. Regardless of the number of separatory flanges 37 utilized, each singles yarn must be brought into contact with other singles yarn on the disc 41 by suitable channeling means, one embodiment of which is illustrated at 42 in FIG. 2.
As further shown in FIG. 3, the channeling means can include guide portions 42a and 42b which serve to deposit the yarn directly on the surface of the fixation disc 41 and also serve to maintain the yarn on the disc long enough to fix the nodes. The disc can be driven by an electrical motor having an output shaft 43. Although FIG. 2 illustrated a wheel 25 having a single rotation means 41, such wheel can be provided with a plurality of such fixation means distributed around the wheel, it being understood that each such fixation means should be positioned to contact a node.
False-twist jets suitable for use in the system of FIG. 1 are shown in FIGS. 4 and 5, these also being disclosed in the aforementioned application.
As shown therein, each jet includes a body 50 having a central bore 51 with tangential orifices 52 and 53 intersecting the bore at diametrically opposite sides thereof. Two such jet inlets are provided to permit control of twist in either direction, as by alternately supplying the orifices with air under pressure. Air is supplied through conduits 54 or 55, which conduits are held in place by mounting means such as a plate 56 to which the conduits are attached, the plate being attached to the jet as by screws or similar fastening means 57.
Annular inserts 58 and 59 are provided at opposite ends of bore 51, each insert having an outer diameter equal to the inner diameter of the bore so that the inserts are slidably received therein. Each insert has an interior axial bore 60 of a smaller size than the bore 51, bores 60 being of a suitable size to permit the yarn to longitudinally pass therethrough. Body 50 is provided with internally threaded radially extending bores 61 and 62 which receive set screws 63 and 64, respectively. Bores 61 and 62 extend from the outer surface of the body into bore 51 so that, when inserts 58 and 59 are present, the set screws engage the inserts and hold them in place. Thus, for any given set of circumstances, the inserts can be axially adjusted and then locked in place using the set screws.
By adjustment of the inserts inwardly toward the jet orifices, a position can be established at and beyond which jet will operate in a filming mode on a particular yarn size, substantially regardless of the tension of the thread line. This is due to the fact that the jet orifices are always effectively outside the yarn arc turning radius, the air film resulting from the orifices being recessed radially beyond the insert bores producing a thicker air film. With this structure, the tangential relationship of the orifices 52 and 53 relative to bore 51 is not nearly so critical as in convenient vortex jets. However, it is preferred that the orifices be tangential to bore 51. Jets fabricated as described have been known to develop the same direction twist in yarns with no tension whatsoever and on those strained almost to the point of breakage.
In the manufacture of carpet using yarn manufactured on machines incorporating the features described in connection with FIGS. 1-5, it is common practice to produce yarn on several such machines for supply to a single carpet machine. This is done because of relative production rates and also because of color selection.
It has been found, however, that it is extremely difficult to produce yarns on several spinning machines in such a way that all of the yarns are exactly alike. The twist jets and/or air supplies in different spinning machines can be different enough so that the degree of twist differs in the finished yarns. When these yarns from different machines are tufted into the same carpet which can have, for example, 1,000 yarns in a 12 foot carpet width, these relatively small differences can show up as a streak effect in the final carpet. Thus, if one yarn has a different appearance from its neighbor in a tuft row, and if this appearance is continued row after row, the result is a line or streak warpwise in the carpet which is visually readily apparent, degrading the appearance of the carpet and such carpet is a "second".